An LED light engine may include an LED chip and may be configured to emit light of a color other than a color emitted by the LED chip. For example, a phosphor may be used to convert the light emitted from the LED chip to produce a desirable emission color. The particular phosphor may be selected depending on the wavelength emitted by the LED chip, and the overall color/wavelength of the light to be emitted by the light engine.
In one configuration, for example, a blue light LED chip may be combined with an LED optic made of a clear (transparent) polymer having a relatively high index of refraction, such as silicone. A phosphor (for example, a YAG:Ce phosphor) that converts the blue light from the LED chip having a first wavelength range to yellow light having a second wavelength range may be mixed with the polymer to provide volumetric blue light conversion. The yellow light emitted by the phosphor may combine with the residual unconverted blue light from the LED chip to produce an overall white emission from the LED light engine.
A portion of the light passing through the phosphor may undergo a Stokes shift as it is converted from one wavelength range to another wavelength range. Thus, phosphor-based LEDs may exhibit a lower efficiency than certain other LEDs due to the heat loss from the Stokes shift. Moreover, the proximity of the phosphor to the LED chip may lead to degradation of the package due to the heat produced by the LED chip and by the Stokes shift. Nevertheless, the phosphor method is a popular technique for manufacturing white LEDs. Accordingly, LED light engines, particularly those that produce white light, require thoughtful design.
Manufacture of LED light engines configured to emit light of a color other than a color emitted by the LED chips may be labor and time intensive. For an apparatus having a plurality of such LED light engines, each LED light engine may be assembled by separately attaching each LED optic to an associated LED chip. This is a time-consuming process and has the potential to damage the LED chip, as well as the electrical connections thereto, resulting in poor yield. Automation of attachment of the LED optic, such as with a robot or other pick-and-place equipment, may decrease assembly time, but may still be too slow for commercial viability. Additionally, installation and removal of LEDs in end-use applications may also be labor and time intensive, which also may expose the LED apparatus to potential damage.